Technical Field
Embodiments of the invention relate generally to energy storage devices. Certain embodiments relate to sealed, ventilated energy storage devices.
Discussion of Art
Lithium-ion (“Li-ion”) rechargeable batteries are widely used as they offer relatively high energy densities and good recharge rates. One particular application for these batteries is in vehicles having regenerative braking systems, such as hybrid haul trucks and other hybrid off-highway vehicles (“OHVs”) that are used for surface mining operations, underground mining operations, or the like.
Hybrid OHV applications require a battery technology capable of very high charge rates and simultaneously high capacity of energy storage. Currently, Li-ion battery technology is the only technology capable of meeting the high charge rates and maintaining sufficient life. Unfortunately, high charge rates can produce high internal resistive (I2R) losses in the battery, which must be dissipated to prevent the battery cells from overheating. Maximum cell operating temperatures for Li-ion is typically 55-65 deg C., however the maximum ambient temperatures in which OHV trucks operate can reach 55 deg C., with the majority of operation in ambient temperatures reaching 45 deg C. As a result, there is very little thermal headroom available between the cell temperature and maximum ambient temperature.
Known cooling approaches for Li-ion cells include liquid cooling and indirect air ventilation. In general, liquid cooling is not preferred for OHV applications due to potential failure modes resulting in loss of cooling medium (e.g., water or liquid coolant leaks). Typically, the liquid cooling approach has involved aluminum or copper plates sandwiched between individual Li-ion cells. At least one cold plate (with liquid cooling pipes) is then closely attached to at least one surface of each sandwiched plate to conduct heat. Heat dissipated within the cells is first conducted to the sandwiched plates, and then carried via the plates to the liquid-cooled cold plate, or plates. A liquid cooling medium then carries the heat to a heat exchanger where the heat is ultimately dissipated into the ambient air. In indirect ventilated systems, aluminum or copper plates are similarly sandwiched between cells. The liquid-cooled cold plate is replaced by one or more finned heat sinks. In both approaches, the cold plate or heat sink limits the achievable energy density of the cooled energy storage device.
Therefore, it is desirable to have a cooled energy storage device with higher energy density than has been achieved using the known modes of cooling.